Television synchronization



Dec. 16, 1941. F. BELOW ETAL 2,265,979

TELEVISION SYNCHRONIZATION Filed Aug. 10, 1938' 75 Defies/fay dysfe I Ag. 5

INVENTOR. I

FRITZ BELOW JOHANNES GUNTHER BY GWW A ORNEY;

Patented Dec. 16, 1941 TELEVISION SYNOHR'ONIZ A'TION Fritz Below and Johannes Giinther,-Berlin-Z ehlendori', Germany, asslgnors to the firm of Fernseh Aktien Gesellschaft, Zehlendorf near Berlin, Germany Application August 10, 1938, Serial Nth 224,095 In Germany August 17, 1937 '1 Claims.

invention relates toa method of synchronizing transmitters and receivers for television.

It is known in the art to transmit synchroniz- Figure 1 is applied; Figure 3 shows the output of the network shown in Figure 2; Figure 4 shows ing impulses for synchronization of scanning wave generators in receivers with those at a transmitter, and to transmit such synchronizing impulses during periods in which nopicture signals are transmitted. It is common practice to use the so-called retrace periodfor this purpose. It is also known to transmit two types of im pulses for synchronization of the-vertical and horizontal scanning generators, respectively.

these impulses being of equal amplitude and.dif-.

fering merely in their duration. The duration of the synchronizing impulse for the vertical scanning, hereinafter referred to as the framing impulse, usually exceeds the duration of a scanning line by several times. Inasmuch as the horizontal or line scanning generator is preferably synchronized at the end of each line, also during the occurrence of the framing impulse, in order to avoid drifting of the horizontal scanning wave generator, special measures are .necessary to secure line synchronization during this time. Ithas been proposed, for instance, to serrate a framing impulse at periodic intervals, and to insert line synchronizing impulses in the serrations, or to serrate the synchronizing impulses at periodic intervals and to synchronize the line scanning generatorsat one edge of the serrations.

These methods are dimcult to make operate satisfactorily and involve considerable amount of.

apparatus. a s

It is the object of this invention to provide a simple and emcient method of fram synchronization avoiding the disadvantages o the abovementioned methods, and to provide a simple means of impulse selection. Other objects and advantages of the invention will become apparen from the follo n work to which the series ofimpulses shown in the output of the same network for a slightly modified input Figure shows an amplitude selecting stage which selects the timing impulses for the vertical scanning generator.

.The' invention may now be explained in detail.

' Figure 1 shows a series of synchronizing impulses, the short impulses being for line synchronization, the'impulse of longer duration a framing impulse. The line synchronizing impulses may have a duration of 10% of a line period,

while the framing impulse extends over 150% of the line period. This may represent the signal available at the receiver after demodulation of the carrier if wirelessly transmitted. This signal is fed through a network as showri in Figure 2, comprising a capacitance'land a resistor 2.

For television transmission at 441 scanning lines, frames per second and an interlaced ratio of 2 1, and line synchronizing duration of 10% of a line period, the value of the capacitance I maybe made approximately 1,000 micromicrofarads, and that of resistance 2 approximately 50,000 ohms, These values render a time constant at which the line synchronizing impulses will remain substantially undistorted when passing through the network. The framing impulsesof longer duration, however, will become considerably distorted, as Figure 3 illustrates, which represents the output of the network according to Figure 2 taken across resistance 2. It may be seen that the trailing edge of the framing impulse of Figure 1 gives rise to a' peak 3 in Figaccomplished on the basis of difference in J The broad idea of this invention is to mix framing impulsesof a duration in the order of one scanning line period with line synchronizing impulses of equal amplitude and polarity, but of considerably shorter duration; to apply this series ofmixed impulses to a network possessing such frequency characteristics that the edges of the framing impulses wilt produce a peak opposite to the'flrst mentioned polarity, and to utilize these for synchronization ofv the vertical scangenerator attire-receiver. a Referring to :the drawing, Figure 1 shows a synchronizing impul es intersp rsed a r-raining impulse; Figure 2 shows the net-* following line synchronizing impulse also proure 3, which can be used-for synchronization of the vertical scanning generator. This peak impulse is of opposite polarity to the line synchronizing impulses so that discrimination between framing andline synchronizing impulses can be polarity.

i For interlaced scanning, it is preferable to limit the duration of framing impulses to less than one-half scanning line period in order to avoid coincident occurrence of line synchronizing and framing impulses. This secures synchronization of the horizontal scanning generator withoutany of the special measures mentioned in the foregoing. The output of the network for framing impulses of a duration of'less than one-half scanning line period is shown in Figure 4. Again the trailing edge of the received framing impulse produces an impulse. However, the immediately duces an impulse in the same direction which differs from the first impulse only in amplitude. In this case it is, therefore, preferable, for perfect separation, to employ a discriminator circuit, for which an over-biased amplifier stage may be used. Such an arrangement is shown in Figure 5. The coupling condenser land grid leak resistor 2 constitute the network shown in Figure 2. The output of the network is directly applied to the control grid or screen grid of an amplifier tube 4. The bias of tube 4 is so chosen that the tube does not draw current on the peak impulses caused by line synchronizing impulses. I

The plate circuit of tube 4 is capacitatively coupled to the vertical scanning generator 6 at the terminal 5.

It may be understood that networks other than.

that shown in Figure 2 may also be used to accomplish the same results. I In fact, any network 20 5. A television scanning system comprising a network including impedance elements and .being which substantially suppresses all frequencies below a frequency greater than the vertical scanning frequency, and lower than the horizontal scanning frequency, will produce the required resuits.

What we claim isz' 1. In television, the method of synchronizing a scanning operation comprising the steps of transtially undistorted, and causing said impulses of longer duration to produce impulses having a polarity opposite to said first named polarity upon passing through said network, and utilizing only saidimpulses -of opposite polarity to synchronize said scanning operation.

2. In television, the method of synchronizing a scanning operation comprising the steps of transmitting a series of impulses of equal amplitude andpolarity, certain impulses possessing a longer duration than others, applying said series of impulses to a network allowing the impulses of short duration to pass through saidnetwork substantially undistorted, and causing said impulses aof'longer' duration to produce impulses having} a' polarity opposite to said first named polarity upon passing through said network, applying the resultant series of impulses to a first scanning'wave-generator sensitive to impulses of one polarity onlyvand applying the same result ant series lof-impulses'to a second scanning wave generator sensitive to impulses of the opposite polarity only.

3. In television,- the method of synchronizing a scanning operation comprising the" steps of transmitting a series of impulses of equal amplitudeand polarity, certain impulses possessing a longer duration than others, applying said series of impulses to a network allowing the impulses of short duration to pass through said network substantially'undistorted, and causing said impulses at longer duration to produce impulseshaving apolarity opposite to said first named polarity ,upon passingthrough said network, applying the resultant series of impulses-to a ,vertical 'sca'nning wave generator in such polarity thatit responds to saidimpulses of opposite pol- 10 ing longer durations than others, said impedance elements being so proportioned as to permit passage through said network of the impulsw of shorter duration substantially without distortion thereof and to render said network so responsive to said impulses of longer duration as to derive therefrom impulses having a polarity opposite to that of the applied impulses, and means for utilizing only said impulses of opposite polarity to synchronize scanning operations in said system.

2 ing longer durations than others, said impedance elements being so proportioned as-to provide a time constant of the order of the durationof said impulses having longer durations, thereby to derive from said impulses of longer duration im- 80 pulses having a polarity oppositetothat' of the applied impulses, and means for :utilizing only said impulses of opposite polarity. to synchronize scanning operations in said system. y

6. A television scanning system ,jcornprising a 85 network includirifcapacitantbe and resistance elements connectedin series relation and being adapted to have applied thereto a series of impulses of substantially equal amplitudes andvof the same polarities,- certain of; said impulses havi40 ing longer durations than others saideimpedance elements being so proportioned as ta permit passage through said network of the impulses of shorter duration substantially without distortion thereof and to cause said impulses of longer duration .to develop across said resistance element impulses having a polarity opposite tpfthat of the applied impulses, .and means for" utilizing only said impulses of opposite polarity to' synchronize scanning operations in said-:sys'tem.

7,. A television scanning system comprising a network including impedance elements and being adapted to have applied thereto aseries of impulses, of substantially equal amplitudes and of the'same polarities, certain of said impulses hav-- ing'longer durations than others, said p dance (50 ration to develop across one of: said impedance elements impulses having a pglarityopposite to that of the ,appliedimpulses and-initiated by the trailing edges of ;said applied impulses aof longer duration, and means for utilizinggoply said im- 65 pulses of opposite polarity tofsynchronize scanning operations in said system.

FRITZ isnrbw. JoHAmgEs GiiNTHER. 

